Nipah virus (NiV) and Hendra virus (HeV) are closely related paramyxoviruses that comprise the Henipavirus genus (Anonymous 1999 MMWR Morb Mortal Wkly Rep Ward, J. W. ed. 48:335-337; Chew, M. H. et al. 2000 J Infect Dis 181:1760-1763; Chua, K. B. et al. 2000 Ann Neurol 48:802-805; Eaton, B. T. 2001 Microbes Infect 3:277-278; Goh, K. J. et al. 2000 N Engl J Med 342:1229-1235; Lee, K. E. et al. 1999 Ann Neurol 46:428-432; Lim, C. C. et al. 2000 Am J Neuroradiol 21:455-461; Murray, K. et al. 1995 Science 268:94-97). Paramyxoviruses are negative-sense RNA containing enveloped viruses and encompass a variety of important human and animal pathogens, including measles virus, mumps virus, Sendai virus, Newcastle disease virus, rinderpest virus, canine distemper virus, human parainfluenza viruses, respiratory syncytial virus, and simian virus 5 (reviewed in Lamb and Parks, 2007, Fields Virology, eds. Knippe & Howley, Lippincott, Williams & Wilkins, pp. 1449-1496).
Like other paramyxoviruses, HeV and NiV possess two major membrane-anchored glycoproteins in the envelope of the viral particle. One glycoprotein is required for host cell receptor recognition and attachment and is designated as either a hemagglutinin-neuraminidase protein (HN), a hemagglutinin protein (H), or in the case of henipaviruses, a glycoprotein (G), which has neither hemagglutination nor neuraminidase activities. The other major glycoprotein is the fusion (F) glycoprotein, which is a trimeric class I fusogenic envelope glycoprotein containing two heptad repeat (HR) regions and a hydrophobic fusion peptide (Fp). The henipavirus F glycoprotein is synthesized as a precursor F0 that undergoes posttranslational cleavage by host cell Cathepsin L that occurs within the endosomal compartment, most likely during endocytosis and recycling of F to the mature fusiogenic F1 (a larger carboxy terminal fragment) +F2 (a smaller amino terminal fragment) subunits that are held together by disulfide bonds through conserved cystine residues. See Pager, C. T. et al. 2006. Virology 346: 251-7; Pager, C. T. et al. 2005. J Virol 79: 12714-20; Meulendyke, K. A. et al. 2005, J Virol, 79: 12643-9; Diederich, S. M. et al. 2005, J Biol Chem, 280: 29899-903. In the mature form of F, the Fp's are situated at the N terminal of F1 followed by the first HR (HRA) and the second HR (HRB) is located at the C terminus of F1 preceding its transmembrane domain (reviewed in Lamb and Parks, 2007, Fields Virology, eds. Knippe & Howley, Lippincott, Williams & Wilkins, pp. 1449-1496).
Following attachment to host receptor ephrin (EFN) B2 or B3 via the G glycoprotein, HeV and NiV infect cells through a pH-independent membrane fusion process. This process is still poorly understood and is believed to involve conformational changes in G upon receptor binding that leads to activation and triggering of F. Lamb, R. A. et al. 2006, Virology, 344:30-7; Steffen, D. L. et al. 2012, Viruses, 4:280-308. Upon triggering, F undergoes significant conformational rearrangements that facilitate the insertion of the fusion peptide into target membranes, bringing the two HR regions together in the formation of the six-helix bundle structure or trimer-of-hairpins during or immediately following fusion of virus and cell membranes. The F driven membrane fusion process is thought to involve an irreversible folding from a metastable form followed by subsequent discrete conformational changes to a lower energy state. Several molecular details of this F re-folding upon triggering have been revealed in the structural solutions of both post- and pre-fusion conformations of respirovirus F. Yin, H. S. et al. 2005, Proc Natl Acad Sci USA, 102(26): 9288-93; Yin, H. S. et al. 2006, Nature 439:38-44.
Although currently there are no clinically approved vaccines or therapeutics against HeV or NiV, a Henipavirus G glycoprotein specific neutralizing monoclonal antibody (mAb) m102.4 was shown to protect African green monkey against HeV from lethal disease when it was administered as late as 72 hours post infection. Bossart, K. N. et al. 2011, Sci Transl Med, 3:105ra103. Antibodies or antibody fragments, such as monoclonal antibodies (mAbs) and fragments thereof, can be useful in elucidating the structure of a protein and understanding the function associated with various domains as well as providing a potential reagent for use as prophylaxis and/or therapeutic agents as in the case of the anti G m102.4. To date, there are very few reported anti henipavirus F mAbs and none are produced from recombinant protein. Aguilar, H. C. et al. 2007,J Virol, 81:4520-32; Guillaume, V. H. et al. 2006, J Virol, 80:1972-8. These reports provide limited information concerning the specific properties of the isolated antibodies. The development of a neutralizing anti-F antibodies and antibody fragments could serve as another potential henipavirus infection therapeutic agent perhaps more effectively when combined with m102.4. The anti-F antibodies and antibody fragments could also provide valuable tool to facilitate in structural and functional characterization of F mediated fusion in henipaviruses.
Therefore, the development of neutralizing or inhibiting antibodies and antibody fragments against NiV and HeV could have important implications for prophylaxis and passive immunotherapy. In addition, the characterization of the epitopes of the antibodies and antibody fragments and the mechanisms of neutralization and inhibition of NiV and HeV infection could provide helpful information for development of candidate vaccines and drugs. Finally, such antibodies and antibody fragments could also be used for diagnosis and as research reagents.